Current Research

Friday, October 18, 2013

Nonhuman Primate Handedness: Is there is a population-level preference?

Do you write with your left hand or right hand? When ask to open a jar, do you use your left or right hand? A handful of "tasks" can be used to determine your hand preference. Just because someone uses their right hand to write doesn't automatically makes them a right-handed person; some cultures frown upon left hand use and taught left-handed children to write with their right hand.

Humans are usually righties (right-handed), preferring to use their right hands for most manual tasks. Most, I said, because there are instances where reaching over with the closest hand would suffice. About 70% to 90% of the world population is right-handed. Then you have the lefties (left-handed) who basically are going to hell because they are the devil's minion (no, not really LOL!). Sprinkled among them are the ambidextrous, those that use their left and right hand with no preference. But is this true in nonhuman primates? Ever wonder if other primates have hand preference like we do?

Handedness is due to the lateralization of the brain hemispheres (Knecht et al., 2000). Individuals that are right-handed have a more dominant left brain hemisphere, while those that are left-handed have a more dominant right brain hemisphere. In most humans (Homo sapiens), the left brain hemisphere is more dominant, thus the majority of the human population is right-handed (Knecht et al., 2000). The human left brain hemisphere is also involved in language and is where Broca’s area and Wernicke’s area are located (Knecht et al., 2000). Broca’s area is involved in speech production while Wernicke’s area is involved in language comprehension. Lateralization results in a preference for handedness in humans (Knecht et al., 2000). That is, an individual is left-handed or right-handed due to brain lateralization, while ambidextrous individuals are not lateralized at all.

A meta analysis by McGrew and Marchant (1997) on hand laterality in nonhuman primates concluded that nonhuman primates do not show patterns of hand preference. Instead, the authors claim that even though individuals might be lateralized and have a preference for either left or right hand, there is no evidence that hand preference exists in population-level. The only nonhuman primates that have a population bias in handedness are chimpanzees (Pan troglodytes) but are from captive populations (McGrew & Marchant, 1997). The authors claim that patterns of handedness in nonhuman primates cannot be used as a theoretical framework for the evolution of handedness and brain lateralization in humans because only few primates display handedness and most are from captive settings (McGrew & Marchant, 1997).

A study by Vauclair et al (2005) found that olive baboons (Papio anubis) have a population-level preference for right handedness when performing bimanual tasks but no significant preference in handedness when performing unimanual tasks. Later, Meguerditchian & Vauclair (2006) found that olive baboons (P. anubis) have a preference for right handedness when communicating. Specifically, olive baboons use their right hands to hand slap when presented with agonistic stimuli by experimenters. Subsequent study on communicative gestures and non-communicative actions in olive baboons suggests that preference for right handedness may be due to the left brain hemisphere dominance, and that lateralization may have favored right handedness in communicative gestures as opposed to pure motor functions in unimanual tasks (Meguerditchian & Vauclair, 2009).

McGrew W.C., & Marchant L.F. 1997. On the Other Hand: Current Issues in and Meta-Analysis of the Behavioral Laterality of Hand Function in Nonhuman Primates. Yearbook of Physical Anthropology 40:201–232.